Will giant wood spider Nephila pilipes respond to diet variation by altering silk protein? Evidence from field surveys and manipulative studies.
Orb-weaving spiders were well-known to alter orb-building behaviour, web structure or silk output to qualitative or quantitative prey variations. Recent studies demonstrated that orb-weaving spiders may also adjust pigments, sticky substances and even silk protein to foraging variation. In this study we examined whether food composition affects dragline silk gene expression of the giant wood spider Nephila pilipes thus changes the amino acid composition of dragline silk. The most abundant amino acid residues of major ampullate silk are analine, glycine and proline. In a feeding experiment spiders' intake of these amino acids was manipulated then the changes in amino acid composition of silks were observed. In addition, the foraging history of a N. pilipes population was recorded for ten days. After the recording the dragline silk from the spiders were collected and the correlation between prey intake and dragline silk amino acid composition was assessed. Moreover, dragline silks were collected from eight N. pilipes populations in Taiwan to see whether a spatial variation in amino acid composition of dragline silks also existed. The prey compositions of four of the populations were also compared. The results of food-manipulation experiments showed that amino acid compositions of these dragline silks were consistent among individuals receiving different treatments. Although individual N. pilipes in the field ingested different prey, their dragline silk composition did not exhibit significant variation. Amino acid composition of dragline silks collected from four populations whose prey composition were available also showed no significant difference. However, a significant variation was found when dragline silks collected from eight populations were compared. Among the amino acids compared, only glutamate and glycine exhibited significant difference but the variations only ranged from 1% to 2%. Since results from food manipulative studies showed that diet seemed to exert no effect on dragline silk composition of N. pilipes, the observed variation might resulted from rapid evolution of spidroin genes. While Nephila can alter web structure and silk output in responding to foraging variation, their dragline silk protein seemed to be optimized to a fixed composition.
Updated: Mar-10-2014 01:22:51 (Taiwan, GMT+08:00).